00:01
Okay, i want to find f -dashed of x first.
00:05
Let's write this f -fx as x -square to minus 36 power of negative 1.
00:14
Then f -dashed of x would be negative 1 times x squared minus 36 to minus 2, and by the chain rule, times that by 2x.
00:32
So what i get then is minus 2x over x squared minus 36, a whole thing squared.
00:44
And that's f dash of x.
00:51
Now, my domain of f of x were up here, the key thing in math is you can't divide by zero.
01:05
So that bit can't be zero.
01:07
So it's going to be all real numbers are minus negative 6 and 6.
01:17
In other words, all numbers except for 6 and minus 6 will work.
01:22
For those two numbers, give you 0 on the bottom...